Previous methods for recovering precious metals from a flotation concentrate involve smelting the concentrate to produce a "matte" in which metals values are further concentrated. The matte is then subjected to a series of leaching steps to leach out the base metals. Generally, a separate leaching step is used for each base metal to be removed. The precious metals are then leached out and removed from each of the leaching solutions in subsequent recovery steps.
The traditional process described above has several shortcomings. Firstly, smelting is generally an environmentally undesirable process because of the gasses given off and the problem of disposal of solid residue. Furthermore, if the concentrate has a high magnesia content, the melting temperature of the concentrate may be too high to be effectively smelted. Still furthermore, using a plurality of leaching steps is relatively costly and some of these steps also contribute to further environmental contaminants.
U.S. patent application Ser. No. 08/089,088, filed on Jul. 8, 1993 and now issued as U.S. Pat. No. 5,364,444, which is hereby incorporated by reference herein, discloses a process (hereinafter referred to as the "new process") in which all of the precious metals and various additional metals are dissolved as one of the process steps. The precious metals are separated from solution leaving a solution containing iron, copper, nickel and various contaminants such as magnesium, aluminium, calcium and sodium. Each of the solutes is present as the respective metal chloride in an acidic solution. It is an object of the present invention to remove the iron, copper, and nickel individually from the solution, subsequently to remove the contaminants from the solution and then to convert the remaining solution to hydrochloric acid which may be re-used in the initial process.